1. Field of the Invention
The present invention relates to a processing method for a wafer having a circular recess on the back side of the wafer and an annular projection surrounding the circular recess, wherein the annular projection is removed from the wafer by this method.
2. Description of the Related Art
In a semiconductor device fabrication process, a plurality of crossing division lines called streets are formed on the front side of a substantially disk-shaped semiconductor wafer (which will be hereinafter referred to also simply as a wafer) to thereby define a plurality of separate regions where a plurality of devices such as ICs and LSIs are formed. The semiconductor wafer is cut along the streets by using a cutting apparatus, thereby dividing the wafer into a plurality of individual semiconductor chips (devices).
Prior to cutting the wafer along the streets, the back side of the wafer is ground to reduce the thickness of the wafer to a predetermined thickness. In recent years, it has been required to reduce the thickness of the wafer to a smaller value, e.g., about 50 μm, in order to achieve the miniaturization (reduction in size and weight) of electrical equipment. Such a thin wafer lacks stiffness like a sheet of paper and it is difficult to handle, so that there is a possibility of damage to the wafer during transfer. To cope with this problem, there has been proposed a grinding method in Japanese Patent Laid-open No. 2007-19461, for example, wherein the back side of a wafer having a device area and a peripheral marginal area surrounding the device area on the front side is ground to form a circular recess in only a central portion corresponding to the device area, so that a reinforcing annular projection is formed around the circular recess on the back side of the wafer so as to correspond to the peripheral marginal area.
As a method of dividing such a wafer along the streets (division lines), the wafer having an annular projection on the back side along the outer circumference of the wafer, there has been proposed a method including the steps of removing the annular projection and next cutting the wafer along the streets from the front side thereof by using a cutting blade (see Japanese Patent Laid-open No. 2007-19379). In Japanese Patent Laid-open No. 2007-19379, the step of removing the annular projection is disclosed as a method of grinding the annular projection to remove the same or a method including the steps of circularly cutting the boundary between the circular recess corresponding to the device area and the annular projection and next removing the annular projection from the device area.